26 Apr 2019 - Researchers point toward marine creatures’ inability to adapt to changing water temperatures, lack of adequate shelter.
As Mark Kaufman reports for Mashable, the analysis—centered on around 400 cold-blooded species, including fish, mollusks, crustaceans and lizards—suggests marine creatures are ill-equipped to adapt to rising temperatures and, unlike land animals that can seek shelter in the shade or a burrow, largely unable to escape the heat.
“You don't have anywhere to go,” Natalya Gallo, a marine ecologist at the Scripps Institution of Oceanography who was not involved in the study, tells Kaufman. “Maybe you can hide under a kelp leaf, but the entire water around you has warmed.”
Speaking with National Geographic’s Christina Nunez, lead author Malin Pinsky, an ecologist and evolutionary biologist at Rutgers University in New Jersey, further explains that ocean dwellers “live in an environment that, historically, hasn’t changed temperature all that much.”
Given that cold-blooded creatures rely on their surroundings to regulate body temperature, relatively stable marine ecosystems have actually made their inhabitants more susceptible to significant temperature changes. And while ocean temperatures are still much lower than those on land, as Anthony J. Richardson and David S. Schoeman point out in an accompanying Nature News and Views piece, marine heat waves, increased carbon dioxide pollution and other products of global warming are driving Earth’s oceans to higher temperatures than ever before.
To assess the threat posed by warming waters, Pinsky and her colleagues calculated “thermal safety margins” for 318 terrestrial and 88 marine animals. According to Motherboard’s Becky Ferreira, this measure represents the difference between a species’ upper heat tolerance and its body temperature at both full heat exposure and in “thermal refuge,” or cooled down sanctuaries ranging from shady forests to the depths of the ocean.
The team found that safety margins were slimmest for ocean dwellers living near the equator and land dwellers living near the midlatitudes. Crucially, Nunez writes, the data revealed that more than half of marine species at the higher end of their safety margins had disappeared from their historical habitats—a phenomenon known as local extinction—due to warming. Comparatively, around a quarter of land animals had abandoned their homes in favor of cooler environments.